This invention relates to a thermoelectric cooler for making ice or frozen treats or for cooling a relatively small amount of food or beverage.
A thermoelectric ice maker for making molded ice blocks is described and claimed in U.S. Pat. No. 4,587,810 issued May 13, 1986, to Fletcher and in U.S. Pat. No. 4,487,024 issued Dec. 11, 1984 to Fletcher et al. The ice maker described in U.S. Pat. No. 4,587,810 uses a shallow heat conductive tray, i.e., a metal tray, to hold a flexible bag having individual compartments as mould compartments for ice blocks. The shallow walls of the tray are surrounded with insulation and the lid of the ice maker which covers the tray immediately above the freezer bag is also insulated. The bottom of the tray is cooled with a plurality of thermoelectric elements.
Thermoelectric units have low cooling rates and are able to maintain only a limited hot surface/cold surface temperature differential. Condensation around thermocouples can be a problem. Providing a cost effective unit of this type that provides efficient freezing and cooling would be very desirable. Further, a unit that is subject to minimum condensation and in which means are provided to remove any condensation to a location where it will not cause later problems such as deterioration of the semiconductor materials or short circuiting of electric circuits would be very desirable from a long term standpoint.
It is believed that an attempt has been made in the ice maker of U.S. Pat. No. 4,578,810 and U.S. Pat. No. 4,487,024 to overcome these problems but it is believed that, because the thermoelectric elements are placed under the cooling tray, natural convection will not enhance the action of fans dissipating heat withdrawn from the tray. This fact appears to have been recognized by the inventor since he tilts his tray at an angle to the horizontal for various stated reasons. No particular measures appear to have been taken to reduce condensation.
It would also be very desirable that a small scale and cost effective freezer for use, for example, in individual rooms in offices, hotels, cars, etc., might also be capable of providing ice blocks of various sizes in bags or other forms, frozen treats, or a small number of individual cooled beverages. The inventor of U.S. Pat. No. 4,587,810 and U.S. Pat. No. 4,487,024 has not attempted to provide any cooling compartment sufficiently deep and spacious that freezing of various shapes and formats of ice blocks or frozen treats and cooling of beverages or small amounts of other food substances may be contemplated. Nor have they attempted to provide a dual purpose device which is capable of uniformly freezing a plurality of ice blocks or uniformly cooling one or more single serving beverages while providing a means to prevent the latter from freezing.
The present inventors have attempted to devise a compact, multipurpose ice maker/cooler of small size suitable for use by individuals at convenience locations. Moreover the present inventors have attempted to provide such a cooler utilizing a minimum number of thermoelectric elements to minimize initial cost of the device and to minimize running expenses. The present inventors have recognized the desirability of maintaining a uniform cooling temperature within the ice maker/cooler. It has not previously been thought possible to provide uniform temperature within a thermoelectric cooler when utilizing only one thermoelectric element. Moreover, in coolers of small size problems of uniform temperature and rapid cooling of freshly inserted contents are greater than in larger coolers.
In addition, the present inventors have recognized the desirability of keeping the hot side (or heat sink) of the thermoelectric module at or very close to ambient in order to take full advantage of the limited temperature differential available from the thermoelectric module.
A further problem exists concerning the heat sink. When the cooler is turned off there is a tendency for heat to flow back into the cooler. The present inventors have also addressed this problem.
Accordingly the present invention provides a compact multipurpose ice making cooler comprising a box having an insulated front compartment having an insulated compartment lid and a heat conductive liner continuous over a bottom liner wall and front, rear and side liner walls, the liner defining a cold chamber having a height greater than the distance between the front and rear liner walls; a thermoelectric module for cooling the liner, the module being in thermal communication, on the one hand, with the liner and, on the other hand, with a heat sink to dissipate heat from the liner, the module and heat sink being located behind the rear liner wall such that natural convection tends to dissipate said heat, the heat sink projecting into a rear compartment having air vents to the exterior; a fan in the rear compartment to supplement dissipation of said heat; a thermistor to continuously monitor operation of the thermoelectric module; and a dual set point controller with built-in hysteresis to control the temperature within the cooler in dependence on one of two preset desired temperatures depending on the position of a user activated slide switch.
The thermoelectric module may be spaced from the rear wall of the liner by a spacer block, the spacer block and the module being imbedded in insulation on the rear wall, and sealed to prevent the ingress of condensation.
The heat sink advantageously comprises a vertical bank of horizontal fins projecting rearwardly into the rear compartment. A front face of the bank of fins may lie flush with the insulation on the rear wall of the front compartment and in thermal contact with the thermoelectric module.
The liner may advantageously be formed of xc2xc inch aluminum plate or other material suitable for good thermal conductivity and the thermistor is advantageously located on one of the side walls or the front wall so that it controls the temperature at a distance from the thermoelectric module.
In order to minimize sudden rise in temperature within the cooler when fresh, unfrozen, contents are inserted, a thermal ballast may be used. The thermal ballast may be located outside the cooling chamber and inside the insulation. It may be any high specific heat material e.g. a thermal gel confined around the cooling chamber or maybe a block, or blocks, of thermal gel material contacting the outer surface of the cooling container within the insulation. Other materials such as blocks of aluminum (possibly embodied as a thickened cold chamber wall over all or part of its surface), other metals, other liquids e.g. water or alcohol solutions may also be used. However practical considerations such as ease of achieving good thermal transfer with the cold chamber, ability to easily adapt to the shape of any cavity between the cold chamber and the insulation, cost, weight, and leakage and environmental considerations must be taken into account. While the thermal ballast is described herein as it relates to the present ice maker/cooler, one skilled in the art will appreciate that the thermal ballast can be advantageously applied to many similar apparatus such as any thermoelectric or traditionally chilled freezer or cooler to improve its thermal stability.
Means may be provided to maintain the fan running for a period after the thermoelectric module is turned off to dissipate heat within the heat sink into the ambient air, thereby reducing the temperature of the heat sink and the temperature differential between the heat sink and the cold chamber. This will reduce the natural flow of heat back into the cold chamber.
Moreover, even when the thermoelectric module is xe2x80x9coffxe2x80x9d, a small forward voltage may help to prevent the back flow of heat from the heat sink to the cold chamber. While this means of blocking heat flow back through the thermoelectric module while it is turned off and dissipating it into the ambient air is described herein as relating to the present ice maker/cooler, one skilled in the art will appreciate that this technique can be advantageously applied to any thermoelectric freezer or cooler to substantially improve overall efficiency.
Also taught is a cooler further having a beverage dispensing door located proximal to the bottom of the front and wherein the liner walls are adapted to form a beverage stack. Preferably, the bottom liner wall is contoured to contact a greater surface area of a bottommost beverage container. In another preferred embodiment, the cooler has an indicator means to alert a user when only one or two beverage containers remain in the cooler. Preferable, the invention provides a can dispensing actuator located proximal to the bottom liner wall and a control arm articulating between the door and the actuator, whereby, upon opening the door, the control arm moves the actuator such that the actuator ejects a bottom beverage container and holds a second bottom beverage container within the stack. The actuator may move around a pivot point. A spring can be fitted to the door for closing the door.